Electronic devices continually are reduced in size and weight, particularly portable electronic devices. One example of such a portable electronic device is a portable communication device such as a pager or a radiotelephone.
Reduction in size and weight provides convenience for the user. Smaller electronic devices are more easily carried and thus may be used in more applications in more locations. Smaller lighter electronic devices are designed for easy, portable use.
One technique for reducing size of electronic devices is providing more than one housing containing the operational circuitry. A movable housing element is provided which can be collapsed or folded against another housing element to reduce the size of the electronic device in a stowed position, and extended or unfolded to an operational position. Examples of such electronic devices include foldable radiotelephones of the type having a hinged keypad cover and of the clam shell type.
However, during use of foldable housing elements, operational circuitry in the separate housing elements must communicate. For example, radiotelephones with hinged keypad covers have included a microphone or an antenna in the keypad cover which must be electrically coupled to the main radio circuit in the main housing. Flexible circuit elements, or flex strips, or flex, have been developed to convey electrical signals using metallic conductors on a flexible substrate.
As electronic devices continue to shrink, the desire has remained to more evenly distribute the operational circuitry between multiple housing elements. This means flexible circuit elements must have more conductors or traces to handle increased number of signals. More conductors increase the width of the flexible circuit element. However, wider flex strips create additional problems of routing between housing elements and of termination to a printed wiring board (PWB).
In one known clam shell radiotelephone design, a hinge element between upper and lower housings is interrupted to provide a flex barrel routing a flex between the housings. This radiotelephone uses a stationary, externally exposed housing for the routing of the flex as well as a stationary shaft, on which a movable housing pivots. Use of so many elements complicates the assembly and thereby increases the manufacturing cost of the radiotelephone. Moreover, the flex circuit is still visible where it passes from the flex barrel to the housing. Since it is visible, it is also susceptible to damage and can detract from the appearance of the radio.
At the printed wiring board, the flex strip must be electrically terminated. Connectors such as a zero insertion force (ZIF) connector have been developed to mechanically receive the end of a flex strip and create an electrical connection between conductors or traces on the flex and conductors on the PWB. However, the spacing of the electrical conductors on the ZIF connector is limited by manufacturing tolerances. The current limitation is typically 0.50 mm conductor pitch. When used with flex having a large number of traces, such a connector is too large for practical use. A flex strip with 30 traces requires a connector more than 15 mm wide. This is too large to accommodate on a PWB of many small electronic devices. Moreover, routing a flex strip 15 mm wide may not be mechanically possible, given the small size of mechanical features.
Accordingly, there is a need in the art for improved method and apparatus for routing flexible circuit elements in electronic devices.